Control Device And Pump Apparatus

ABSTRACT

This invention relates to programmable electronic device that prevents wastewater submersible and non-submersible pumps as well as viscous pumps from ragging therefore avoiding pump blockage. In one aspect the invention provides a pump apparatus comprising a pump and a control device for a pump, the pump being a mechanically switched pump such as a direct online/star delta pump and capable of being operated in a forward and a reverse direction, the control device comprising: a monitoring mechanism to monitor the torque of the pump, a control mechanism to control the direction of the pump and being capable of selectively directing the pump to (i) stop, (ii) operate in a reverse and (iii) operate in a forward direction; wherein the control mechanism is adapted to control the pump to do at least one of (a) stop and (b) operate in a reverse direction when the monitoring mechanism detects a pre-determined value in the torque of the pump. The device is programmed to provide anti-ragging functionality whilst providing traditional electrical pump protections. The physical size of the device has been minimised which enables great use and, significantly, retro-fitting of the product.

This invention relates to a control device for pumps and to a pumpapparatus comprising the control device.

Pump blockages contribute a significant cost to water authoritiesoperational spend by having to attend site to unblock to avoid floods tothe local area and associated damage of reputation if they occur.

It would be beneficial to mitigate the amount of maintenance used forcertain pumps, especially those pumping wastewater.

Moreover, it would be beneficial to improve the power efficiency ofpumps.

An object of the present invention is to mitigate the maintenancerequirements and/or improve the power efficiency of pumps.

U.S. Pat. No. 6,254,353 discloses a method and apparatus for controllingoperation of a submersible pump and discloses a variable speed pump,evidenced by FIG. 2 which shows a rectifier circuit and a 3 phaseH-bridge.

According to a first aspect of the present invention, there is provideda pump apparatus comprising a pump and a control device for a pump, thepump being a mechanical switched pump and capable of being operated in aforward and a reverse direction, the control device comprising:

a monitoring mechanism to monitor the torque of the pump,

a control mechanism to control the direction of the pump and beingcapable of selectively directing the pump to (i) stop (ii) operate in areverse direction and (iii) operate in a forward direction;

wherein the control mechanism is adapted to control the pump to do atleast one of (a) stop and (b) operate in a reverse direction when themonitoring mechanism detects a pre-determined value in the torque of thepump.

Thus the present invention claims a mechanically switched pump, ratherthan a relatively complex variable speed pump shown in U.S. Pat. No.6,254,353. Moreover, the present invention monitors the torque of thepump whereas U.S. Pat. No. 6,254,353 monitors the frequency of the pump(as detailed in e.g. FIG. 11, FIG. 13 and claim 1). The inventor of thepresent invention has discovered an important benefit of such anapproach. The present invention can detect when a pump is labouring (butthe output is not necessarily changing) because of a blockage startingto occur, and can take remedial action at this early stage. In contrastrelying on monitoring the frequency of a pump will only suggest ablockage when the pump is unable (not merely labouring) to maintain thedesired frequency, which will often be when the blockage is more severe.Embodiments of the present invention therefore can take remedial actionat an earlier stage of a blockage, which is more effective at clearingthe blockage and/or minimising the time taken to clear the blockage.

A mechanical switched pump is one which is activated by a mechanicalswitch and so can take up the forward, stop, or reverse modes. Suitablemechanically switched pumps include direct online pumps or Star/Deltapumps.

In contrast, soft start and Variable Speed Drive (VSD) pumps can ramp upgradually the speed of the pump and are not mechanically switched pumps.

The pump may have a power rating less than 25 kw, optionally less than(but not totally restricted to less than) 9 kW, sometimes less than 7.5kw.

According to a second aspect of the present invention, there is provideda pump apparatus comprising a pump and a control device for a pump, thepump having a power rating of less than 25 kw, optionally less than 9kW, more optionally less than 7.5 kw and capable of being operated in aforward and a reverse direction, the control device comprising:

a monitoring mechanism to monitor the torque of the pump,

a control mechanism to control the direction of the pump and beingcapable of selectively directing the pump to (i) stop (ii) operate in areverse direction and (iii) operate in a forward direction;

wherein the control mechanism is adapted to control the pump to do atleast one of (a) stop and (b) operate in a reverse direction when themonitoring mechanism detects a pre-determined value in the torque of thepump.

The pump according to the second aspect of the invention is typically amechanically switched pump.

According to a third aspect of the present invention there is provided amethod of fitting a control device as herein described to a pump asherein described. Indeed, the present invention allows control devicesto be retro-fitted to pumps in situ.

The response of the control mechanism when the monitoring mechanismdetects a pre-determined value in the torque of the pump is preferablyinitially to control the pump to (a) stop. That is, power to the pump isstopped and the pump is allowed to coast to a rest. Preferably the pumpis then put into a reverse direction. The pump may be stopped again andput into a forward direction.

Preferably the control mechanism is adapted to direct the pump into aseries of reverse and forward cycles normally with a user adjustablestopping period of 0-30 s but not limited thereto between directionchanges. This allows the pump to come to a rest before direction changeand so reduces stress on the pumps.

More preferably the control mechanism is adapted to direct the pump intoa series of reverse and forward cycles (normally with said delaysbetween forward and reverse directions) of the pump until a furtherpre-determined value of pump torque is reached. The first and secondpre-determined values are often the same although may be different. Thusin use, when the torque is noted to be, for example, above a certainvalue, then the pump would be directed to a reverse and preferably toproceed through a series of reverse, then forward, then reversedirections, until the torque detected by the monitoring mechanism isbelow a pre-determined value or the number of clean attempts exceeds apredefined maximum attempts.

Typically each stage in the cycle (forward and reverse) lasts for 3 to20 seconds

The monitoring mechanism typically measures the torque of the pump bymeasuring the current at which the pump is operating. When the currentis increased this is indicative of rag or blockage on the pump which isinhibiting its operation. Once the rag causes an increase in currentabove the pre-defined level, the control mechanism will proceed toreverse (preferably cycle from reverse forward and back with time delaybetween direction changes) to remove debris causing the rag.

As the current demanded by the motor is directly proportional to torque,the inventor considers this the most suitable variable to monitor.Nevertheless a torque instrument could be put on the motor's shaft inthe well although this may have a slower reaction time and so is lesspreferred.

The monitoring mechanism may also be adapted to monitor the pump currentwith regard to potential overloading of the pump.

Standards for excess current being directed to pumps are often imposedby regulatory authorities to safeguard overheating. These limits, whichdepend on a number of different variables, can be stored by the deviceand the control mechanism may be adapted to control the pump or anotherdevice in response to an overload breaching a pre-determined safetylevel, which is indicative of the pump overheating. Other devices thecontrol mechanism may control include alarms. Preferably the controldevice, comprising the components for monitoring the torque of the pumpand the components adapted to monitor the potential overloading of thepump are provided on the same device.

Thus the monitoring mechanism to monitor the output of the pump and themonitoring mechanism to monitor the thermal stability of the pump may beprovided on the same device.

Any feature of any aspect of the present invention may be combined withany other feature of any other aspect of the present invention.

The monitoring mechanism may also comprise a monitoring means to detectany sudden change or short circuit in the current supplied to the motor,and the control mechanism is normally adapted to suitably respond tosuch an event, for example by shutting down the pump.

The pump may be a pump for pumping viscous fluids such as sewage andsludge, wastewater, grit etc.

Preferably on start-up, the pump proceeds through a reverse and forwardcycle. Preferably the pump starts at full power, without a restrictionin power supplied, optionally with reverse and forward cycle immediatelyafter start-up.

An advantage of certain aspect of the invention is that pump may becleared of debris without manual intervention, reducing pump downtimeand costs associated with pump maintenance.

A further advantage of certain embodiments of the invention is that thepumps may be more efficient because the rag on them may be cleared morefrequently than using manual intervention.

A further advantage of certain embodiments of the invention is that thecontrol device may be provided on a single device, thus saving space.

Moreover it is very useful to allow such a device to be retro-fitted,and certain embodiments benefit from this feature.

The cycle(s) of reverse and forward pumping actions described herein maybe referred to as anti-ragging functionality.

The device may be programmed to provide anti-ragging functionalitywhilst providing traditional electrical pump protections. The physicalsize of the device has been minimised which enables greater use of theproduct. Preferably the size is less than 104 mmH×45 mmW×200 mmD .

The device is particularly useful for small to medium pumping stations,such as those operated with pumps having a power of less than 9 kW,optionally less than 7.5 kw.

Traditionally larger pumping stations would be controlled with VariableSpeed Drives (VSD) which is less preferred to the smaller (<9 kW)mechanically switched pumps preferred in the present invention.

An advantage of certain embodiments of the invention is that the pumpapparatus of the present invention may be less expensive to manufacture,compared with VSD devices, which may be ten times the cost of mechanicalswitching devices. Thus embodiments of the invention provide a benefitof having a responsive pump control without the expense of a VSD system.A benefit of certain embodiments is that this functionality is providedin the same device used to monitor the potential overloading of the pumpapparatus and so additional functionality may be provided to the pumpapparatus within the, often limited, confines of the existing pumpapparatus.

Thus embodiments of the invention provide de-ragging functionalitysomewhat akin to VSD at a fraction of the cost therefore, making it moreeconomical for smaller stations. Also, the device is preferably designedto be retro-fitted into existing stations and is physically much smaller(<250 cm²) than any VSD.

The device can be easily retro fitted into existing starter panels as itreplaces thermal/electronic overload devices. The system monitors thecurrent in real time and upon a slight over current can begin ade-ragging sequence.

The sequence is completely customisable and the event that triggers thesequence can be changed or more events can be added i.e. on each startevent.

Pumps used in the present invention should be capable of being operatedin the forward or reverse direction. This includes pumps where theexisting control system only functions to direct them in a forwarddirection and a stop position and not a reverse direction.

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying figures, in which:

FIG. 1 is a flowchart showing the stages of a device in accordance withthe present invention;

FIGS. 2 and 3 are views of an embodiment in accordance with the presentinvention,

FIG. 4 is a circuit diagram indicating electrical connections and atypical retro-fit installation.

The device 10, shown in FIGS. 2-3, is a hardware and software solution.The device measures real time current on the three conductors supplyinga pump via current transducers (CT's). From this current, the deviceknows the loading of the motor during operation.

During commissioning of the pump the low and high current consumptionsare recorded. A set point of around 10% is added to the high level and10% subtracted from the low level. These set points are entered into thedevice to provide the pre-determined “activation level”.

As shown in FIG. 1, the pump is first turned on 1 and it will runthrough a start-up clean cycle for a pre-determined number of directionchanges of a pre-defined duration 2. The pump then runs as normal 3,until an increased load on the pump is detected 4 by the motor drawing ahigher level of current. This is indicative of the motor's torqueincreasing because it is attempting to maintain speed against a largerforce, such as ragging. The clean cycle then starts by cutting power tothe pump, 5. Typically the inertia of the pump and the fluid continuingto pass therethrough will keep the pump running in the same directionfor a short period of time after the power is cut—the pump will “coast”to a rest. Thus after the power is cut to the motor it will wait 5 for apre-defined time A before progressing to the next step. The time A canbe varied by the user and is typically larger for larger pumps.

After this time the pump goes into reverse, 6, also for a forpre-defined time B which may also be varied by the user. The pump stopsagain 7 by cutting power and allowing it to coast to a rest. After afurther period of time A the pump goes into a forward direction forpre-defined time C.

The above clean cycle (steps 5 to 8) is repeated for pre-defined numberof times, which again may be varied by the user. At this point the cleanends and the device has a number of options.

If the rag is cleared, indicated by a normal current being demanded bythe motor in the forward direction, then it will resume pumping asnormal, step 3. If not, the device will attempt to clean again byreverting to the clean cycle (steps 5 to 8). The device will continue onthis cycle until a maximum number of clean cycles is met at which pointit would trip the pump, 9.

The maximum number of cleans allowed counter will be reset after thepump has finished pumping.

Thus as noted above, when the pump is under or more likely above normaloperation, if the “activation level” is met, a clean cycle is theninitiated on the motor. The clean cycle is fully customisable butconsists of but not limited to and not necessarily in the order of;forward rotation for a user adjustable time, reverse rotation for useradjustable time. The number of direction changes and duration can bechanged by the user. If the device is unable to return the pump to isoriginal loading tolerance band after a user defined number of tries,the motor will trip an alarm.

As the real time current of the pump is monitored the device also actsas motor protection as it contains a thermal image algorithm of themotor. This will allow the device to act like a traditional motorthermal overload.

An advantage of certain embodiments of the present invention is thatthey provide an economical de-ragging solution for small to mediumwastewater pumps where the unit detects a change in current andimmediately reverses the pump to dislodged debris built up during normalflow.

Due to its physical size, the device of certain embodiments of theinvention have been designed to be retro-fitted into existing pumpcontrol panels.

FIG. 4 shows a circuit diagram for the FIG. 1 embodiment and illustratesthe ease at which the present device can be retrofitted to an existingpump. The pre-existing pump motor 20 is supplied by a three-phase powersupply L1, L2, L3. A contactor K1 is provided to engage the motor 20into a forward direction, or to disengage the power from the motor 20and allow it to stop. The system can be modified to utilise anembodiment of the present invention by connecting a contactor K2 inparallel to the switch K1. The switch K2 can be engaged to direct themotor 20 into a reverse direction.

Also added to the existing configuration, downstream of the switches K1and K2 and upstream of the motor 20, is a current sensor 22 to monitorthe current being supplied to the motor 20. The current sensor isconnected to a control system 30.

The control system 30 has an input interface 32, an output interface 34and a power supply 36. The input signals are received and processed bythe input interface 32 and the appropriate outputs are activated, asdescribed above with respect to FIG. 1. The outputs Q1 and Q2 from theoutput interface 34 control the contactors K1 and K2 which in turncontrol the motor 20.

The existing coil connection to the contactor K1 is rerouted to thederagger control system 30 by the use of an interposing relay. Thisprovides the run signal. From there the deragger takes control of thepump 20.

When monitoring the pump current, the device may be activated atprogrammable set points. Moreover the pump may be customisable by theuser.

Improvements and modifications may be made without departing from thescope of the invention. For example applications may be added to thecontrol device, such as to use the pump more intensively during thenight to, or to use the pump for odour control.

1. A pump apparatus comprising a pump and a control device for a pump,the pump being a mechanically switched pump and capable of beingoperated in a forward and a reverse direction, the control devicecomprising: a monitoring mechanism to monitor the torque of the pump, acontrol mechanism to control the direction of the pump and being capableof selectively directing the pump to (i) stop, (ii) operate in a reversedirection, and (iii) operate in a forward direction; wherein the controlmechanism is adapted to control the pump to (a) stop and (b) operate ina reverse direction and direct the pump into a series of reverse andforward cycles of the pump, each forward and reverse stage in the cyclelasting for 1-20 seconds, when the monitoring mechanism detects apre-determined value in the torque of the pump. 2-4. (canceled)
 5. Apump apparatus as claimed in claim 1, wherein the control mechanism isadapted to direct the pump into a series of reverse and forward cyclesof the pump until a further pre-determined value of pump torque isreached.
 6. (canceled)
 7. A pump apparatus as claimed in claim 1,wherein each forward and reverse stage in the cycle lasts for a timeperiod which may be set and varied by a user.
 8. A pump apparatus asclaimed in claim 1, wherein the monitoring mechanism measures the outputof the pump by measuring the current at which the pump is operating. 9.A pump apparatus as claimed in claim 1, wherein the monitoring mechanismis adapted to monitor the pump torque with regard to potentialoverloading of the pump.
 10. A pump apparatus as claimed in claim 1,wherein the control mechanism is adapted to control the pump or anotherdevice in response to an torque breaching a pre-determined level, whichis indicative of the pump overloading or being in danger of overloading.11. A pump apparatus as claimed in claim 1, wherein the control devicecomprising the components for monitoring the torque of the pump and thecomponents adapted to monitor the potential overloading of the pump areprovided on the same device.
 12. A pump apparatus as claimed in claim 1,wherein the pump is a viscous material pump such as a wastewater pump.13. A pump apparatus as claimed in claim 1, wherein on start-up, thepump is adapted to proceed through a reverse and forward cycle.
 14. Apump apparatus as claimed in claim 1, wherein the pump starts at fullpower, without a restriction in the power.
 15. A pump apparatus asclaimed in claim 1, wherein the monitoring mechanism comprises amonitoring means to detect any sudden change in the current supplied tothe motor, and the control mechanism is adapted to respond to such anevent.
 16. A pump apparatus as claimed in claim 1, which is less than 50cm².
 17. A pump apparatus as claimed in claim 1, wherein the pump has apower rating of less than 25 kW preferably less than 9 kW.
 18. A pumpapparatus as claimed in claim 1, comprising a monitoring mechanism tomonitor, directly or indirectly, the thermal stability of the pump,wherein the monitoring mechanism to monitor the torque of the pump andthe monitoring mechanism to monitor the thermal stability of the pumpare provided on the same device. 19-22. (canceled)
 23. A pump apparatusas claimed in claim 1, wherein each forward and reverse stage in thecycle lasts for 3-20 seconds.